Over the past few decades revolutionary advances have been made in electrochemical storage and conversion devices significantly expanding the capabilities and applications of these systems. Current state of the art electrochemical storage and conversion devices implement cell designs specifically engineered to achieve performance attributes enabling requirements and operating conditions supporting diverse applications including portable electronics, transportation, energy, lighting, sensing and communications. Despite the development and widespread adoption of this suite of advanced electrochemical storage and conversion systems, significant pressure continues to stimulate research to expand the functionality of these systems, thereby enabling an even wider range of device applications. The rapid and ongoing growth in the demand for high power portable electronic products, for example, has created enormous interest in developing safer, light weight secondary batteries capable of achieving higher energy densities and cycling performance.
Many recent advances in electrochemical storage and conversion technology are directly attributable to discovery of new materials for key battery components. Lithium battery technology, for example, continues to rapidly develop, at least in part, due to the discovery of novel electrode and electrolyte materials for these systems. From the pioneering discovery and optimization of intercalation host materials for positive electrodes, such as fluorinated carbon materials and nanostructured transition metal oxides, to the development of high performance non-aqueous electrolytes, the implementation of novel materials strategies for lithium battery systems have revolutionized their design and performance capabilities. Furthermore, development of intercalation host materials for negative electrodes in these systems has led to the discovery and commercial implementation of lithium ion secondary batteries exhibiting high capacity, good stability and useful cycle life. As a result of these advances, lithium based battery technology is currently widely adopted for use in a significant range of applications including primary and secondary electrochemical cells for portable electronic systems.
Commercial primary lithium battery systems typically utilize a lithium metal negative electrode for generating lithium ions which are transported during discharge through a liquid phase or solid phase electrolyte and undergo intercalation reaction at a positive electrode comprising an intercalation host material. Dual intercalation lithium ion secondary batteries have also been developed, wherein lithium metal is replaced with a lithium ion intercalation host material for the negative electrode, such as carbons (e.g., graphite, coke, etc.), metal oxides, metal nitrides and metal phosphides. Simultaneous lithium ion insertion and de-insertion reactions allow lithium ions to migrate between positive and negative intercalation electrodes during discharge and charging. Incorporation of a lithium ion intercalation host material for the negative electrode also has the significant advantage of avoiding the use of metallic lithium which is susceptible to safety issues upon cycling attributable to the highly reactive nature and non-epitaxial deposition properties of metallic lithium.
The element lithium has a unique combination of properties that make it attractive for use in high performance electrochemical cells. First, it is the lightest metal in the periodic table having an atomic mass of 6.94 AMU. Second, lithium has a very low electrochemical oxidation/reduction potential (i.e., −3.045 V vs. NHE (normal hydrogen reference electrode). This unique combination of properties enables lithium based electrochemical cells to achieve high specific capacities. Advances in materials strategies and electrochemical cell designs for lithium battery technology have realized electrochemical cells capable of providing useful device performance including: (i) high cell voltages (e.g. up to about 3.8 V), (ii) substantially constant (e.g., flat) discharge profiles, (iii) long shelf-life (e.g., up to 10 years), and (iv) compatibility with a range of operating temperatures (e.g., −20 to 60 degrees Celsius). As a result of these beneficial characteristics, lithium and lithium ion batteries are currently the most widely adopted power sources in portable electronic devices, such as cellular telephones and portable computers. The following references are directed generally to lithium and lithium ion battery systems which are hereby incorporated by reference in their entireties: U.S. Pat. Nos. 4,959,281; 5,451,477; 5,510,212; 6,852,446; 6,306,540; and 6,489,055; and “Lithium Batteries Science and Technology” edited by Gholam-Abbas Nazri and Gianfranceo Pistoia, Kluer Academic Publishers, 2004.
Despite these advances, significant challenges remain to be addressed for the continued development of lithium ion batteries including issues relating to the cost, electrochemical performance and safety of these systems. Advances in cathode active materials, such as LiMn2O4, LiCoO2 and LiFePO4, have accessed improved device performance. [See, e.g., U.S. Pat. Nos. 5,763,120; 5,538,814; 8,586,242; 6,680,143 and 8,748,084]. Such advanced cathode active materials, however, are still limited in the overall energy densities achievable and also bring into play significant issues with overall conductivity, cycling performance and toxicity for some of the materials. High capacity anode active materials, such as nanostructured Si, Sb, Sn, Ge and alloys thereof, access higher specific capacities and allow for elimination of the use of metallic lithium to avoid problems associated with dendritic growth. [See, e.g., US Publication 2013/0252101 and U.S. Pat. No. 8,697,284]. Such advanced anode active materials, however, are susceptible to large changes in volume upon charging and discharge which can cause structural degradation upon cycling resulting in capacity fading, poor cycle life, lower system efficiency and increased internal resistance. Moreover, many commercial lithium ion systems implementing advanced cathode and anode active materials typically exhibit actual specific energies 4 to 12 times smaller that the specific energy of the electrodes due to the significant weight of other battery components such as separators, electrolytes, current collectors, connectors and packaging components.
As will be clear from the foregoing, there exists a need in the art for secondary electrochemical cells for a range of important device applications including the rapidly increasing demand for high performance portable electronics. Specifically, secondary electrochemical cells are needed that are capable of providing useful cell voltages, specific capacities and cycle life, while at the same time exhibiting good stability and safety. A need exists for alternative cell geometries and intercalation based electrochemical cells that eliminate or mitigate safety issues inherent to the use of lithium in lithium ion battery systems.